LATEST ALERT from usability guru Jakob Nielsen: A list of 10 usability violations that are both particularly egregious (conspicuously bad or offensive) and often seen in a wide variety of applications:

Non-Standard GUI Controls
1.a. Looking Like a GUI Control Without Being One

Inconsistency

No Perceived Affordance
3.a. Tiny Click Targets

No Feedback
4.a. Out to Lunch Without a Progress Indicator

Bad Error Messages

Asking for the Same Info Twice

No Default Values

Dumping Users into the App

Not Indicating How Info Will Be Used

System-Centric Feature

Useful note: “Application usability is enhanced when users know how to operate the UI and it guides them through the workflow. Violating common guidelines prevents both… Usually, applications fail because they (a) solve the wrong problem, (b) have the wrong features for the right problem, or (c) make the right features too complicated for users to understand.”